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  • Author or Editor: K. Nahdi x
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Abstract  

The aim of this work is to highlight the importance of controlling the residual water vapour pressure above the sample as well as the rate of the thermal decomposition during the thermal dehydration of cerium cyclotriphosphate trihydrate CeP3O9·3H2O. For this reason, the dehydration of the titled compound was followed by both techniques: the constant rate thermal analysis at P H2O = 5 hPa and the conventional TG-DTA in air. It has been shown that the pathway of the thermal dehydration depends strongly on the nature of atmosphere above the sample. However, in air atmosphere CeP3O9·3H2O decomposes in two well defined steps to give first an amorphous, phase in the temperature range 440–632 K, then the cerium polyphosphate Ce(PO3)3 crystallizing in orthorhombic system (C2221) at T>632 K. Whereas decomposition carried out at 5 hPa water vapour pressure, also occurring in two steps, leads first to a crystallized intermediate monohydrate at 259<T<343 K and second to a crystallized anhydrous cerium polyphosphate, at 343<T<791 K, with a structure different from those of all lanthanide polyphosphate known actually and particularly from that of Ce(PO3)3 obtained in air. The activation energy corresponding to the dehydration of the initial phosphate was also measured experimentally by means of two CRTA curves and was found equal to 81±5 kJ mol−1.

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Abstract  

An instrumental thermal neutron activation analysis facility based, on a 16 Ci241 Am–Be source, a high resolution -ray spectrometry setup and a PC-based data acquisition system at KFUPM is described. The thermal neutron flux distribution was determined from the induced activities of high purity indium foils. The absolute thermal neutron flux was calculated from the activities of bare and cadmium-covered gold foils at a position of 3 cm from the soource at which the flux reaches a maximum. The facility tests were carried out with the determination of manganese concentrations in six types of industrially important steel samples. The result of 1.33% manganese in SS-304 steel sample was in excellent agreement with the literature value. The method is nondestructive, economical and ideal for bulk analysis.

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